The invention relates to a brake disc implemented as a casting.
Brake discs of this type, which are used both in automobiles and in commercial vehicles, are commonly produced from gray cast iron, with the friction ring being materially separated from the neck of the brake disc such that the friction ring can move radially in relation to the neck. This avoids stresses that may occur as a result of the thermally induced radial expansion of the friction ring, with resultant heat cracks.
Brake discs which are produced without sliding elements which separate the friction ring and the neck are also known, in which case the neck is commonly firstly cast and the connection region thereof with the friction ring is provided with a so-called mediator, such that the subsequently cast-on friction ring does not enter into a metallic bond with the neck.
Although this makes different materials pairings possible, the production of such a brake disc is relatively expensive and is therefore effectively unacceptable for the production of a product in series production, as represented by such a brake disc.
Brake discs of this type are known, for example, from EP 1 972 823 A1 or DE 198 43 399 A1.
A further brake disc, also known as a cast brake disc, is disclosed in DE 102 27 529 A1. This document proposes forming the sliding elements as sleeves, of which an inner sleeve is connected fixedly to a pin of the neck with a circular cross section and an outer sleeve guided axially displaceably thereon is fixedly connected to the friction ring, wherein the sliding element, i.e. both sleeves, are concomitantly cast in when the neck and the friction ring are being produced in one piece by casting.
In this case, however, the diameter of the pin and therefore the absorption of the torques which arise during braking are limited to a relatively great extent, since they depend on the thickness of the friction ring or on the associated width of the cooling ducts formed. In order to establish a sufficiently stable connection between the friction ring and the neck, an appropriately high number of connection elements, i.e. of pins and sleeves, are therefore required. These connection elements are formed by the toothed rings within the context of the invention.
Of course, this is only possible with an accordingly high manufacturing outlay and material use, but this is an obstacle to the constant requirement for minimization of the production costs.
DE 195 05 112 A1 discloses and describes a brake disc which, rather than being internally ventilated, has a solid friction ring which is materially separated from the neck by sliding elements, which are formed cohesively from a meandering sheet metal strip. However, the function of this design is limited insofar as it is not suitable for the use of an internally ventilated brake disc.
The invention is based on the object of further developing a brake disc of the above-identified type such that its production is easier and thus more cost-effective, its service life is increased, and its weight is minimized.
This and other objects are achieved by a brake disc, in particular an internally ventilated brake disc, implemented as a casting, comprising a friction ring, which has an inner toothed ring, and a neck, which is materially separated therefrom and is retained such that it cannot rotate by an outer toothed ring which engages into the inner toothed ring, for connection to a wheel hub, wherein cast-in sliding elements are provided between the teeth for radial movement of the friction ring in relation to the neck. Each sliding element has a U-shape, the opposing legs of which are arranged between the radially and axially oriented side faces of the associated teeth which face toward one another. A web of the U-shape, which connects the legs, extends radially.
To begin with, such a novel brake disc is distinguished by its extraordinarily simple production. Thus, the sliding elements, which are formed for example from a sheet metal strip and preferably consist of stainless steel with a higher melting point than that of the cast material of the friction ring and of the neck, can be inserted into the casting mold, to be precise into the casting cores for ventilation ducts of the friction ring.
During the subsequent casting of the brake disc, the sliding elements are concomitantly cast into the brake disc from both outer sides, it being possible in the case of an appropriate design for the friction ring and the neck to be cast in one-piece.
During subsequent material-removing machining, as has been required until now, material is removed from the neck by turning in the radial direction until the included sliding elements are exposed.
As a result, both the outer toothed ring of the neck and the inner toothed ring of the friction ring are formed, and are therefore no longer materially connected to one another. Two separate components which are movable radially with respect to one another are therefore produced by the turning operation.
Appropriate shaping of the sliding elements provides a positive connection between the neck and the friction ring which acts in the axial direction, and for this purpose radially extending beads can be provided in the sliding elements. For example, these radially extending beads permit the radial movement of the friction ring with respect to the neck of 1-2 mm but preclude axial movement to such an extent that this lies merely in a range <0.1 mm.
A further aspect of the invention provides for the sliding element to be formed with two plies, wherein one of the two plies which lie one against the other is held positively on the friction ring and the other ply is held positively on the neck. In this case, too, the configuration is selected such that the friction ring can move radially without obstruction, in which case the planar faces of the two plies which lie against one another then shift with respect to one another.
If the sliding elements are formed with one ply, it is expedient for there to be a coating on one side, with which a connection between the sliding element and the associated casting is prevented.
Each sliding element has a U-shaped outline and surrounds a tooth of the inner toothed ring on three sides, the web which connects the legs oriented in parallel being embedded in the neck and extending radially.
In order to provide the friction ring with the possibility to expand radially in any case, i.e. even in the event of possible warpage of the elements during casting, the legs of the U-shaped sliding element are arranged at an angle with respect to one another in the radial direction, such that a tapered portion or inversely a widened portion is produced in the direction of the central axis. It is preferable for the legs to be inclined by an angle in the range of 10-30° with respect to one another.
Before forming, the sliding element is present in the form of a sheet metal strip in which a wedge-shaped notch in the sense of a cutout is made in that region which forms the web during the subsequent forming, the wedge angle of said cutout corresponding to the angle at which the two legs of the sliding element run with respect to one another. This achieves optimization of the material use, since the blank used can be formed from a rectangular strip, for example by cutting strip material to length.
For the rest, merely compressive forces which depend on braking torques are to be absorbed or transmitted by the sliding elements, in contrast to those according to the prior art, which are subjected to bending, pressure and/or tension.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.